Recently, there has been an increased awareness of possible harm done to the environment when marine oil spills occur. A variety of devices and equipment have been produced for spill clean up, mostly by skimming or other mechanical separation means. Almost all of these devices must be attached to a boat or mounted on other type floating platforms in order to perform spill clean-up tasks.
The single most significant problem in marine oil spill clean-up operations is the physical control and management of floating equipment. The effects of wind, waves, current, or other environmentally induced forces severely limit the utilization of clean-up devices. These operational constraints result from the inability of the operator to maintain a fixed relative position between the skimming apparatus and the surface of the contaminated water.
All equipments currently employed to perform skimming operations are dependent upon the ability to selectively differentiate between water and the material being removed from the surface of that water. The effectiveness of an oil skimming device can be reduced to only a percentage of its capacity when subjected to the forces of the marine environment.
The objective of this invention is to provide a method for overcoming the effects of wind, waves, and current on the operation of surface skimmers and separators. This is accomplished by use of a special purpose vessel that may be rendered stationary and motion compensating equipment attached to the vessel.
We have developed a device that is effective in the deployment, positioning, and operation of equipment used to skim or otherwise remove oil and other contaminants from the surface of water. The use of this device is applicable in all bodies of water and is particularly useful in oceans, bays, estuaries, rivers and lakes. The purpose of this invention is to provide a mounting platform for oil skimming and separation equipment that is capable of being used as a floating, self powered transport device and upon arrival at the spill site, convert to a fixed structure, insensitive to most environmentally induced forces. The invention is equipped with oil skimming and separation devices mounted on motion compensated frames to further improve the operation effectiveness in skimming and separation.
There are several basic types of skimmers commercially available. The following list identifies some types that are applicable for use with this invention:
Boom-skimmer PA0 Disc PA0 Lifting belt PA0 Paddle belt PA0 Rope mop PA0 Sorbent belt PA0 Suction head PA0 Submersed belt PA0 Submersed plane PA0 Vortex PA0 Weir
Selection of an appropriate type of skimmer is based on specific conditions of the spill site including; oil viscosity, depth of oil, wave height, wind velocity, rate of current and water temperature. Change in any one o combination of these factors may alter the preferred selection of skimmer type and require a halt or modification in the logistics of the clean-up operation.
Wave height is a most critical factor on skimmer performance because the wave induced motions in the floating skimmer causes the oil collection mechanism to intermittently lose contact with oil floating on the surface. Simple skimmers such as weirs perform poorly in rough seas because the weir lip is alternately above or below the oil/water interface causing the skimmer to alternately draw in air or water. Boom skimmers with good heave stiffness help to keep the weir at the water surface but short choppy waves alter its performance and cause the device to ingest large quantities of water.
Skimmers with a large inertial mass generally have problems following the oil water interface along the wave cycle. In an attempt to solve this problem, some skimmers have been designed so that the mass of the skimmer in the water is quiet low. In addition, pumps, tanks and other heavy components have been removed from the skimmer and located on the support vessel. Some skimmers have collection elements that offer low mass per unit length characteristics that result in good wave pattern conformance. Rope mops and boom skimmers are good examples of these kinds of devices.
Some skimmers with relatively high inertial masses are able to follow long period wave patterns well. Floating disc skimmers and some specialized weir skimmers operate well in long period conditions.
Lifting belt skimmers and submersion belt skimmers are able to operate in a range of wave patterns in which the waves are not higher than the vertical dimension of their belts. Similarly, submersion plane skimmers can operate in waves that are not higher than the vertical dimension of their submersion planes. Currents affect the performance of skimmers because high currents generally cause the skimmer to be displaced from the optimum position for oil removal and result in the escape of oil under or around the collection device. Also high currents may result in vertical movement of anchored skimming devices and, subsequently, intake swamping and low oil/water recovery ratios.
The performance of all of the listed skimmers may be greatly enhanced by restriction or reduction of motions relative to the surface being skimmed. Our invention removes pitch and roll which are the inherent motions in all floating devices. In addition, our invention utilizes motion compensation techniques that cause the skimming device to more closely follow surface motions. This action results in lower relative displacement between the skimming device and the skimmed surface and higher recovery rates and percentage of efficiency.